Vitamin D3 deficiency is a global phenomenon, which can be coped with supplementation and food fortification. However, vitamin D3 bioaccessibility may depend on factors, such as matrix composition and interactions throughout the gastrointestinal tract. This research focused on the effect of different matrices on vitamin D3 content during digestion, and the effect of pH on its bioaccessibility. The INFOGEST protocol was employed to simulate digestion. Three different types of commercial supplements, two foods naturally rich in vitamin D3, and three fortified foods were investigated. High-Performance Liquid Chromatography was used to determine the vitamin D3 initial content in supplements and foods, as well as after each digestion stage. Results indicated that foods exhibited higher bioaccessibility indices compared to supplements, and a higher percentage retention at the end of the gastric phase. The pH study revealed a positive correlation between increased gastric pH and the corresponding content of vitamin D3. Interestingly, exposing the matrix to low pH during the gastric phase resulted in an increased intestinal content of D3. Vitamin D3 is more bioaccessible from foods than supplements, and its bioaccessibility is susceptible to changes in gastric pH. Fasting conditions (i.e. gastric pH=1) enhances vitamin’s bioaccessibility.
